Ultra-light and ultra-accurate portable coordinate measurement machine with multi-piece joint engagement

ABSTRACT

A coordinate measurement machine (CMM) includes a manually-positionable articulated arm having first and second ends. The articulated arm includes a plurality of arm segments and a plurality of rotary joints. The first end includes a connector configured to connect to a measurement probe. The second end includes a base for mounting the CMM. A housing of at least one rotary joint from the plurality of rotary joints has a cylindrical outer surface that engages a) the base or b) a connecting portion that connects the at least one rotary joint to another rotary joint from the plurality of rotary joints, the housing welded to the base or to the connecting portion.

BACKGROUND

The present disclosure relates generally to a coordinate measuringmachine and more particularly to a high accuracy, ultra-lightweightportable coordinate measuring machine.

Coordinate measurement machines serve to, among other things, measurepoints in a three-dimensional space. Coordinate measuring machines tracethe measuring points in Cartesian coordinate space (x, y, z), forexample. Coordinate measuring machines typically consist of a stand anda tracing system. The stand may serve as a reference point relative towhich the tracing system moves in the space in a measurable manner. Thetracing system for a portable coordinate measuring machine may includean articulated arm attached to the stand at one end and a measurementprobe at the other end.

For the measurement to be useful, it must be accurate. Very highaccuracy, however, is difficult to achieve because of factors such astemperature and load conditions. Particularly in portable coordinatemeasuring machines, warping of the arm caused by thermal changes or bychanges in loads has a negative effect on the measurement's accuracy.Consequently, in terms of their performance, conventional portablecoordinate measuring machines were not nearly as accurate asconventional, non-portable type coordinate measuring machines.

Accuracy Improvements may be available. Conventionally, however, suchimprovements came accompanied by significant increases in mass and/orweight of the coordinate measuring machine. Conventional portablecoordinate measuring machines of improved accuracy were bulky and heavy.These are undesirable characteristics for coordinate measuring machines,particularly portable coordinate measuring machines. Moreover, processesfor constructing and assembling coordinate measuring machines' joints,particularly long joints, with the required precision to obtain accuratemeasurements have not been available.

SUMMARY OF THE INVENTION

The present disclosure provides a portable coordinate measurementmachine (CMM) that is more accurate than prior art coordinate measuringmachines. Remarkably, the CMM disclosed herein is also lighter and lessbulky.

In an aspect of the invention, the CMM disclosed herein includes novelmethods and/or parts for forming portions of the CMM. The housing'sbarrel of at least one rotary joint engages a) the base or b) aconnecting portion of the housing that connects the rotary joint toanother rotary joint. The housing is welded to the base or to theconnecting portion. Welding these parts together is less expensive thanmachining the parts from a single block of steel or casting them in amold. Significantly, the welding approach does not significantly alterthe CMM's precision because any potential imprecision introduced bywelding the parts together may be minimized by using an articulated armerror mapping process (a kinematic model based on a generalizedgeometric error model) to correct the imprecision.

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate various example systems, methods,and so on, that illustrate various example embodiments of aspects of theinvention. It will be appreciated that the illustrated elementboundaries (e.g., boxes, groups of boxes, or other shapes) in thefigures represent one example of the boundaries. One of ordinary skillin the art will appreciate that one element may be designed as multipleelements or that multiple elements may be designed as one element. Anelement shown as an internal component of another element may beimplemented as an external component and vice versa. Furthermore,elements may not be drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrate perspective views of an exemplary coordinatemeasuring machine (CMM). FIG. 1D illustrates a cross-sectional view ofthe exemplary CMM of FIGS. 1A-1C.

FIGS. 2A and 2B illustrate partial exploded and cross-sectional views,respectively, of an exemplary swivel joint of the CMM of FIGS. 1A-1D.

FIG. 3 illustrates an exploded view of an exemplary swivel joint of theCMM of FIGS. 1A-1D.

FIG. 4A illustrates a perspective view of an exemplary housing of aswivel joint.

FIG. 4B illustrates a perspective view of an exemplary block from whichthe housing of FIG. 4A may be formed.

FIGS. 5A and 5B illustrate perspective views of a connecting portion anda barrel portion, respectively, of housing.

FIGS. 6A and 6B illustrate exploded and cross-sectional views,respectively, of a hinge joint of the CMM of FIGS. 1A-1D.

FIG. 7 illustrates a cross-sectional view of an exemplary hinge joint ofthe CMM of FIGS. 1A-1D including a rotary damper.

FIG. 8 illustrates an exploded view of an exemplary base and swiveljoint of the CMM of FIGS. 1A-1D.

FIG. 9 illustrates a perspective view of the exemplary hinge joint ofFIG. 7 mounted to the base and swivel joint of FIG. 8.

FIG. 10 illustrates a perspective view of the exemplary hinge joint ofFIG. 7 mounted to a swivel joint and a base assembly.

FIG. 11 illustrates a cross-sectional view of the exemplary swivel jointand base plate of FIG. 10.

FIG. 12 illustrates an exploded view of the exemplary base plate of FIG.10.

FIG. 13A illustrates a perspective view of an exemplary base assemblyfor a CMM.

FIG. 13B illustrates a perspective view of an exemplary block from whichthe base assembly of FIG. 13A may be formed.

FIGS. 14A and 14B illustrate perspective views of a housing and a baseplate, respectively.

FIG. 15 illustrates a perspective view of an exemplary measurement probeof the CMM of FIGS. 1A-1D.

FIG. 16 illustrates a perspective view of an exemplary on-arm switchassembly of the CMM of FIGS. 1A-1D.

FIG. 17 illustrates a block diagram of exemplary electronics for the CMMof FIGS. 1A-1D.

DETAILED DESCRIPTION

FIGS. 1A-1C illustrate perspective views of an exemplary coordinatemeasuring machine (CMM) 1. FIG. 1D illustrates a cross-sectional view ofthe exemplary CMM 1. CMM 1 includes an articulated arm 2, a base 4, anda measurement probe 6. The articulated arm 2 is attached at one end tothe base 4 and at the other end to the measurement probe 6. The base 4may be attached to, for example, a magnetic holder 5 to attach the arm 2to, for example, a working surface. Articulated arm 2 includes two armsegments 8, 9 and a number of rotary joints 12, 14, 16, 18, 20, 22, 24.The CMM 1 may also include an on-arm switch assembly 10.

The overall length of articulated arm 2 and/or the arm segments 8, 9 mayvary depending on its intended application. In one embodiment, thearticulated arm may have an overall length of about 48 inches. This armdimension provides a portable CMM which is well suited for measurementsnow accomplished using typical hand tools such as micrometers, heightgages, calipers and the like. Articulated arm 2 could have smaller orlarger dimensions.

The rotary joints generally include two types of joints, swivel joints12, 16, 20, 24 and hinge joints 14, 18, 22. The swivel joints 12, 16,20, 24 are positioned generally axially or longitudinally along the arm2. The hinge joints 14, 18, 22 are positioned generally at 90° to theswivel joints or 90° to the longitudinal axis of the arm 2. The swiveland hinge joints are generally paired up as shown in FIGS. 1A-1D but thejoints may be arranged in other configurations. Because of the multiplerotary joints, the arm 2 is manually-positionable meaning that a user isfree to manually move the probe 6 to virtually any position within aradius anchored at the base 4 of the CMM 1. Each of these joints aregenerally shown in FIGS. 2-6A.

In general, the magnetic holder 5 of the base 4 attaches the CMM 1 to aworking surface, the base 4 attaches to the swivel joint 12, whichattaches to the hinge joint 14, which attaches to the swivel joint 16,which attaches to the hinge joint 18, which attaches to the swivel joint20, which attaches to the hinge joint 22, which attaches to the swiveljoint 24, which attaches to the measurement probe 6.

FIG. 2A illustrates partial exploded views of exemplary swivel joint 16while FIG. 2B illustrates partial cross-sectional views of swivel joint16. Each of the figures illustrates only the ends of the swivel joint16; the middle portion of the swivel joint not illustrated correspondsto the arm segment 8. The swivel joint 16 will be used here to describeswivel joints 12, 16, 20, 24 in general even though the swivel jointsmay not be identical. The swivel joints 16 and 20 are very similar.Swivel joint 24 is also similar to swivel joints 16 and 20 except thatswivel joint 24 has a shorter shaft.

The swivel joint 16 may include housings 48, 49, shaft portions 50 a, 50b, and 50 c, bearings 32, 34, encoder PCB 36, encoder disk 38, and slipring 40. The bearings 32, 34 are preferably steel or stainless steelball bearings. The shaft portions 50 a and 50 c may be operably attachedto the ends of the shaft portion 50 b to form a shaft assembly 50. Theshaft portion 50 b, being relatively long, may be fabricated of rigidyet relatively lighter material such as, for example, carbon fiber,aluminum, etc. as well as from steel. The shaft portions 50 a and 50 c,however, may be fabricated of steel to match the material from which thebearings 32, 34 are fabricated. Similar to the relatively long shaftportion 50 b, the tube 60 within which the shaft portion 50 b residesmay be fabricated of the same rigid yet relatively light material asshaft portion 50 b as well as from steel. The swivel joint 16 may alsoinclude covers 62 a-b and various hardware such as the snap rings 64a-c.

At one end of the swivel joint 16, the housing 48 has a barrel portion48 a whose outer surface operably attaches to one end of the tube 60 ofthe corresponding arm segment (arm segment 8 in the case of swivel joint16). The housing 48 also has a shaft connecting portion 48 c thatoperably connects the swivel joint 16 to the previous hinge joint (seeFIGS. 1A-1D). In the case of swivel joint 16, the shaft connectingportion 48 c connects the swivel joint 16 to the shaft of the hingejoint 14. At the other end of the swivel joint 16, the housing 49 has asurface 49 a that operably attaches to a second end of the tube 60 ofthe corresponding arm segment (arm segment 8 in the case of swivel joint16). The housing 49 also has a port 49 b within which an end of theshaft assembly resides, particularly shaft portion 50 a.

As may be best seen in FIG. 2B, at one end of the swivel joint 16, theinner diameter 65 of the port 48 b of the housing 48 engages (e.g.,fixedly attaches to) the outer diameter or outer race of the bearing 32.The port 48 b of the housing 48 may, for example, be glued to the outerdiameter or outer race of the bearing 32. The shaft portion 50 c, forits part, has an outer diameter 67 that engages (e.g., is fixedlyattached to) the inner diameter or inner race of the bearing 32. Theshaft portion 50 c may, for example, be glued to the inner diameter orinner race of the bearing 32. At the other end of the swivel joint 16,the inner diameter 69 of the port 49 b of the housing 49 engages (e.g.,fixedly attaches to) the outer diameter or outer race of the bearing 34.The port 49 b of the housing 49 may, for example, be glued to the outerdiameter or outer race of the bearing 34. The shaft portion 50 a, forits part, has an outer diameter 71 that engages (e.g., is fixedlyattached to) the inner diameter or inner race of the bearing 34. Theshaft portion 50 a may, for example, be glued to the inner diameter orinner race of the bearing 34. The shaft assembly 50, therefore, rotatesabout the axis of rotation a of the bearings 32 and 34 and the housings48 and 49.

The PCB 36 of the swivel joint 16 has installed thereon at least onetransducer configured to output an angle signal corresponding to anangle of rotation of the shaft assembly 50 relative to the housing 48,49 about the axis of rotation a. Each transducer comprises an opticalencoder that has two primary components, a read head 68 and the encoderdisk 38. In one embodiment, two read heads 68 are positioned on PCB 36.In the illustrated embodiment, the encoder disk 38 is operably attachedto an end of the shaft assembly 50 (e.g., using a suitable adhesive)spaced from and in alignment with read heads 68 on PCB 36, which isoperably attached to the housing 48 (e.g., using a suitable adhesive).The locations of disk 38 and read heads 68 may be reversed whereby disk38 may be operably attached to housing 48 and read heads 68 rotate withshaft assembly 50 so as to be rotatable with respect to each other whilemaintaining optical communication. Encoders are commercially availablefrom, for example, Celera Motion under trade names such as MicroEencoders. Each PCB 36 may additionally include a processor for receivingangle signals from the read heads 68, and a transceiver and connector 93for connecting the PCB 36 to the communication bus of the CMM 1 and/orother wiring. Each of the PCB 36 may also include a temperature sensorconnected to the processor to provide for thermal compensation due toroom temperature variation.

The cover 62 b operably attaches to the housing 48 to cover and seal thePCB 36 and encoder disk 38 from dust contamination. The cover 62 aoperably attaches over the cover 62 b and portions of the housing 48 andtube 60 for cosmetic appearance. The cover 62 b has the opening 63 fromwhich the shaft connection portion 48 c of the housing 48 protrudes tooperably connect the swivel joint 16 to the hinge joint 14.

Swivel joint 16 (as well as other joints in CMM 1) may have unlimitedrotation, meaning that it may rotate 360° about its axis of rotation a.Thus, slip ring 40 is used and provides unlimitedly rotatable electricalconnections to swivel joint 16. Shafts used herein in swivel joints suchas the shaft 30 of base swivel joint 12 and the shaft assembly 50 ofswivel joint 16 may be hollow (i.e., have an axial opening 51). Shaftsused herein in hinge joints such as the shaft 80 of hinge joint 18described below may also be hollow and may also include an aperture 81(see FIG. 4B). Back to FIGS. 2A and 2B, as illustrated, the housingcover 62 a has the opening 63, the cover 62 b has the opening 61, andthe housing 48 has the opening 48 d which aligns with the aperture 81 ofthe shaft 80 of the hinge joint 18. Thus, communication bus wiring mayenter the swivel joint 16 from the aperture 81 of hinge joint 14,through the opening 48 d, through the opening 63, the opening 61 andconnect to PCB 36, which connects to the slip ring 40. From the slipring 40, wiring may travel through the axial opening 51 of the shaft 50to the next hinge joint. Such wiring is shown diagrammatically below.

The shaft portions 50 a and 50 c may have grooves 72, 73 machined orotherwise formed thereon. The snap rings 64 b-c may engage the grooves72, 73 to retain the shaft assembly 50 axially in place in relation tothe rest of joint 16 and the bearings 32, 34. Similarly, the housing 49may have a groove 74 machined or otherwise formed thereon. The snap ring64 a may engage the groove 74 to retain the housing 49 axially in placein relation to the rest of joint 16 and the bearings 32, 34. In oneembodiment, instead of or in addition to the combination of the grooves72, 73 and the snap rings 64 b-c to retain the shaft 50 axially in placein relation to the rest of joint 16 and the bearings 32, 34, the shaft50 may be fixedly attached to the inner diameters or inner races of thebearings 32, 34 by use of an adhesive. Similarly, in one embodiment,instead of or in addition to the combination of the groove 74 and thesnap ring 64 a to retain the housing 49 axially in place in relation tothe rest of joint 16 and the bearings 32, 34, the surface 71 of thehousing 49 may be fixedly attached to the outer diameter or outer raceof the bearing 34 by use of an adhesive.

Shoulderless shafts and housings such as those illustrated in FIGS. 2Aand 2B may be manufactured by grinding and honing processes that may bean order of magnitude more precise than machining process used tomanufacture the shouldered or flanged shafts and housings of the priorart. The shoulderless shafts and housings disclosed herein may thus besignificantly more precisely built resulting in significant improvementsin the precision of measurements that may be achieved at the joint 16and similar joints of the CMM 1. In part because of the shoulderlessshafts and housings disclosed herein, the CMM 1 achieves significantlybetter accuracy than prior art portable coordinate measurement machines.

The swivel joint 16 of arm segment 8 is a relatively long joint ascompared to, for example, joint 14 as may be appreciated from FIGS.1A-1D. The bearings 32 and 34 are located far apart. The shaft 50 hasthree parts, the middle portion 50 b having end portions 50 a and 50 cattached to the ends of the middle portion 50 b far apart from eachother. The outer tube 60 is long with housing ends 48 and 49 spaced farapart from each other.

FIG. 3 illustrates an exploded view of an exemplary swivel joint 24.Swivel joint 24 is similar to swivel joints 16 and 20 described aboveexcept that swivel joint 24 has a shorter shaft 50 whose lengthcorresponds to the distance between swivel joint 24 and probe 6 beingshorter than the distance between, for example, swivel joint 16 andhinge joint 18. Thus, the probe 6 rotates about the axis a of the swiveljoint 24 and the swivel joint 24 detects the angle of rotation of theprobe 6, which is attached to the end of the swivel joint 16. See FIGS.1A-1D.

FIG. 4A illustrates a perspective view of an exemplary housing 48 of aswivel joint 16, 20, 24. The housing 48 has a barrel portion 48 a whoseouter surface operably attaches to one end of the tube 60 of thecorresponding arm segment (arm segment 8 in the case of swivel joint16). The housing 48 also has a port 48 b whose inner diameter 65 engages(e.g., fixedly attaches to) the outer diameter or outer race of thebearing 32. The port 48 b of the housing 48 may, for example, be gluedto the outer diameter or outer race of the bearing 32. The housing 48may have a connecting portion 48 c that operably connects the respectiveswivel joint to the previous hinge joint (see FIGS. 1A-1D). In the caseof swivel joint 16, for example, the connecting portion 48 c connectsthe swivel joint 16 to the shaft of the hinge joint 14.

The housing 48 may be manufactured from a single block of material(e.g., steel). FIG. 4B illustrates a perspective view of an exemplaryblock 480 from which the housing 48 may be formed (e.g., machined). Inanother embodiment, the housing 48 may instead be casted as a singlepiece using a mold. Forming the housing 48 as a single piece (e.g., froma single block of material such as the block 480) may offer significantadvantages, the most significant of which may be precision. Forming thepart as a single piece—versus various parts attached together—may reducethe chances of distortion, misalignment, imperfections, etc. that couldnegatively affect the part's precise shape. This is why, in the priorart, parts such as the housing 48 were built (e.g., machined) from asingle block of material. Manufacturing a relatively complex part suchas the housing 48 from a single block of material, however, isrelatively expensive. But, in the prior art, there was no choice.

FIGS. 5A and 5B illustrate perspective views of a connecting portion 48c and a barrel portion 48 a, respectively. The barrel portion 48 a iscylindrical having inside thereof the port 48 b that engages at leastone of the bearings 32, 34. The connecting portion 48 c connects therespective rotary joint to another rotary joint. Unlike the housing 48of FIG. 4A, the housing of FIGS. 5A and 5B would be formed by firstmachining the barrel and connecting portions 48 a, 48 c individuallyfrom blocks smaller than the block 480 of FIG. 4B. The resulting barreland connecting portions 48 a, 48 c may then be welded together. For thispurpose, the connection portion 48 c may have an engagement portion 48cc having a concave semi-cylindrical shape that matches the radius ofthe cylindrical surface of the barrel portion 48 a. The connectingportion 48 c and barrel portion 48 a may be held in place with theengagement portion 48 cc adjacent the cylindrical surface of the barrelportion 48 a and welded together.

As described above, welding the connecting portion 48 c and barrelportion 48 a may negatively affect the precision of the resultinghousing 48 by, for example, distorting the precision honed bore of theport 48 b. Therefore, the welding approach disclosed herein iscounterintuitive in the context of CMM, where there is an expectation ofa high level of precision. However, as it turns out, the benefits ofthis novel approach are significant. For example, it takes 36% less timeand material to machine the two-piece housing of FIGS. 5A and 5B versusthe one-piece housing 48 of FIG. 4A. Also, the two-piece part can bemachined easier. For example, the barrel portion 48 a may be machined ona CNC Lathe while the connection portion 48 c may be machined in a CNCMilling machine. On the other hand, the one-piece housing 48 of FIG. 4Amay need to be machined in a 4 or 5 axis CNC Milling machine, a muchmore difficult and expensive process.

After machining the connecting portion 48 c and barrel portion 48 a, thetwo pieces may be welded together with the engagement portion 48 ccadjacent the cylindrical surface of the barrel portion 48 a. The partsmay be welded together using one of the various known welding methods(e.g., MIG welding, TIG welding, Laser Welding, etc.) In one embodiment,Laser Welding is preferred as it causes the least material distortion.The bearing bore can be honed prior to Laser Welding as Laser Weldingwill not distort the precision honed bore of the port 48 b.

The resulting, welded housing 48 is significantly less expensive than asingle machined part. The resulting, welded housing 48 is also strongerthan a single, casted part that tend to be porous and less strong thanmachined parts. The resulting, welded housing 48 is also less expensivethan a molded part because casting requires major investment in molds.Furthermore, casting often requires post-casting machining, increasingthe cost per part.

The two-piece welded housing 48 of FIGS. 5A and 5B may, by itself, beless precise than the one-piece machined part of FIG. 4A. The use ofsuch a two-piece part is, therefore, again, counterintuitive in thecontext of precision CMM. The invention disclosed herein minimizes anyimprecision of the two-piece housing 48 over the single-piece housing 48by using an articulated arm error mapping process (a kinematic modelbased on a generalized geometric error model) to correct theimprecision. An example of such a mapping process is disclosed in Zhao,Huining & Yu, Lian-Dong & Jia, Hua-Kun & Li, Weishi & Sun, Jing-Qi.(2016), A New Kinematic Model of Portable Articulated CoordinateMeasuring Machine, Applied Sciences, 6, 181, 10.3390/app6070181, whichis hereby incorporated by reference in its entirety. Tests show thatimplementation of such a mapping process results in highly precise CMMmeasurements even when incorporating two-piece, welded housing 48.

FIG. 6A illustrates an exploded view of exemplary hinge joint 18 whileFIG. 6B illustrates a cross-sectional view of hinge joint 18. The hingejoint 18 will be used here to describe hinge joints 14, 18, 22 ingeneral even though the hinge joints may not be identical. At least someof the components of hinge joint 18 are substantially similar tocomponents discussed in detail above in reference to swivel joints 12and 16 and thus these similar components are identified in FIGS. 6A and6B with the same reference designators as in the previous figures.

The hinge joint 18 may include housing 78, shaft 80, bearings 32, 34,encoder PCB 36, and encoder disk 38. The housing 78 has an opening 78 bto which the shaft of the previous swivel joint (shaft 50 of swiveljoint 16 in the case of hinge joint 18) connects. The hinge joint 18 mayalso include covers 82 a-c and various hardware such as the snap rings64 a-c and cap 66.

As may be best seen in FIG. 4B, the housing 78 has ports 87 that engage(e.g., fixedly attach to) the outer diameters or outer races of thebearings 32, 34. The ports 87 of the housing 78 may, for example, beglued to the outer diameter or outer race of the bearings 32 and 34. Inthe embodiment of FIGS. 6A and 6B the housing 78 has two ports 87. Theshaft 80, for its part, has an outer diameter 85 that engages (e.g., isfixedly attached to) the inner diameter or inner race of the bearings32, 34. The shaft 80 may, for example, be glued to the inner diameter orinner race of the bearings 32, 34. The shaft 80, therefore, rotatesabout the axis of rotation b of the bearings 32 34 and the housing 78 ofthe hinge joint 18.

Similar to the swivel joints discussed above, the PCB 36 of the hingejoint 18 has installed thereon at least one transducer configured tooutput an angle signal corresponding to an angle of rotation of theshaft 80 relative to the housing 78 about the axis of rotation b. Eachtransducer comprises an optical encoder that has two primary components,a read head 68 and the encoder disk 38. In the illustrated embodiment,two read heads 68 are positioned on PCB 36. In the illustratedembodiment, the encoder disk 38 is operably attached to an end of theshaft 80 (e.g., using a suitable adhesive) spaced from and in alignmentwith read heads 68 on PCB 36, which is operably attached to the housing78 (e.g., using a suitable adhesive). The locations of disk 38 and readheads 68 may be reversed whereby disk 38 may be operably attached tohousing 78 and read heads 68 rotate with shaft 80 so as to be rotatablewith respect to each other while maintaining optical communication.

The cover 82 b operably attaches to the housing 78 to cover and seal thePCB 36 and encoder disk 38 from dust. The covers 82 a and 82 c operablyattach to each other at one end of the shaft 80 and the cap 66 caps tothe opposite end of the shaft 80 to protect the bearings.

Communications bus wiring may enter the hinge joint 18 from the axialopening 51 of the shaft 50 of the previous swivel joint through theopenings 78 b, 78 c of the housing 78. The wiring may then connect tothe PCB 36 and depart the hinge joint 18 through the axial opening 80 aand the aperture 81 of shaft 80. Such wiring is shown diagrammaticallybelow.

The shaft 80 may have grooves 72 machined or otherwise formed thereon.The snap rings 64 b-c may engage the grooves 72 to retain the shaft 80axially in place in relation to the rest of joint 18 and the bearings32, 34. Similarly, the housing 78 may have a groove 74 machined orotherwise formed thereon. The snap ring 64 a may engage the groove 74 toretain the housing 78 axially in place in relation to the rest of joint18 and the bearings 32, 34. In one embodiment, instead of or in additionto the combination of the grooves 72 and the snap rings 64 b-c to retainthe shaft 80 axially in place in relation to the rest of joint 18 andthe bearings 32, 34, the shaft 80 may be fixedly attached to the innerdiameters or inner races of the bearings 32, 34 by use of an adhesive.Similarly, in one embodiment, instead of or in addition to thecombination of the groove 74 and the snap ring 64 a to retain thehousing 78 axially in place in relation to the rest of joint 18 and thebearings 32, 34, the ports 87 of the housing 78 may be fixedly attachedto the outer diameters or outer races of the bearings 32, 34 by use ofan adhesive.

Shoulderless shafts and housings such as those illustrated in FIGS. 5Aand 5B may be manufactured by grinding and honing processes that may bean order of magnitude more precise than machining process used tomanufacture the shouldered or flanged shafts and housings of the priorart. The shoulderless shafts and housings disclosed herein may thus besignificantly more precisely built resulting in significant improvementsin the precision of measurements that may be achieved at the joint 18and similar joints of the CMM 1. In part because of the shoulderlessshafts and housings disclosed herein, the CMM 1 achieves significantlybetter accuracy than prior art portable coordinate measurement machines.

In one embodiment, structural elements of the joints of the arm 2 may befabricated of steel matching the material from which the bearings 32, 34are fabricated. Structural elements in this context refer to housings28, 48, 49, and 78, shafts 30, 50, and 80, and shaft portions 50 a and50 c. These are the structural elements that are in contact with theinner or outer race of the ball bearings 32, 34. The housing 48 alsoattaches a swivel joint to the next hinge joint. Steel in this contextincludes stainless steel and has a thermal expansion coefficient in therange of between of 9.9 to 18 μm/m° C. at 25° C. The use of relativelyheavy steel for the structural elements of the joints of the arm 2 mayseem somewhat counterintuitive because one of the important features ofthe CMM 1 is that it must be lightweight. Steel is significantly heavierthat the materials used by prior art coordinate measurement machinessuch as aluminum. Structural elements matching the material (i.e.,steel) from which the bearings 32, 34 are fabricated, however, wouldhave the same (or nearly the same) thermal expansion coefficient (i.e.,would expand or contract with temperature at the same rate) as thebearings 32, 34. This minimizes variation in the joint's rigidity overtemperature and thus maintains accuracy of measurements taken over theoperating temperature range of the CMM 1.

In another embodiment, structural elements of the joints of the arm 2,other structural elements such as shaft portion 50 b, tubes 60, etc. andeven non-structural elements of the CMM 1 may be fabricated of acontrolled expansion alloy lighter in weight than steel but having athermal expansion coefficient matching that of chrome steel or 440Cstainless steel (i.e., in the range of between of 9.9 to 18 μm/m° C. at25° C.). A commercially available example of such controlled expansionalloy is Osprey CE sold by Sandvik AB of Sandviken, Sweden. Structuralelements fabricated from materials matching the thermal expansioncoefficient (i.e., would expand or contract with temperature at the samerate) of the bearings 32, 34 minimize variation in the joint's rigidityover temperature and thus maintain accuracy of measurements taken overthe operating temperature range of the CMM 1. The significantly thinnerarm segments 8 and 9 fabricated from rigid yet relatively light materialsuch as, for example, carbon fiber or controlled expansion alloycombined with structural elements (and even non-structural elements)fabricated from controlled expansion alloy result in a CMM 1 that issignificantly lighter and significantly more accurate over the operatingtemperature range than prior art coordinate measuring machines.

FIG. 7 illustrates a cross-sectional view of exemplary hinge joint 14.Hinge joint 22 is very similar to hinge joint 18 described above. Hingejoint 14 is also similar to hinge joints 18 and 22, a significantdifference being that the hinge joint 14 includes a rotary damperassembly. In the illustrated embodiment of FIG. 7, the rotary damperassembly is an instrumented assembly 90 a as described in detail below.To ease the use of the arm 2, a counter balance arrangement in the formof the rotary damper assembly 90 a may be provided to offset the torqueapplied by the weight of the articulated arm. The counter balanceprevents the articulated arm 2 from falling down rapidly due to its ownweight if the user releases it.

The assembly 90 a includes the rotary damper 92 which may be acommercially available rotary damper such as WRD dampers manufactured byWeforma Dampfungstechnik GmbH of Stolberg, Germany. In one embodiment,the rotary damper 92 is a unidirectional rotary damper that providescontrolled damping of rotational movement of the shaft about the axis ofrotation in one direction of rotation. The assembly 90 a may alsoinclude damper hub 94, damper sleeve 96, and torque sensor shaft hub 98,which together form an Oldham coupling. The assembly 90 a may alsoinclude torque sensor shaft 100. The assembly 90 a may also includespacer 102, mount 104, and hardware such as bolts.

The damper assembly 90 a comes together by first coupling a portion ofthe torque sensor shaft 100 to the shaft 80 of the hinge joint 14. Aportion of the torque sensor shaft 100 may be inserted in and fixedlyattached to (e.g., by using adhesive) the axial opening 80 a of theshaft 80. The mount 104 is coupled to the housing 78 of the hinge joint14 by inserting bolts and threading them into threaded openings in thehousing 78. The rest of the components of the rotary damper assembly 90a are then stacked in order: the shaft hub 98 on the shaft 100, thedamper sleeve 96 on the shaft hub 98, the damper hub 94 on the dampersleeve 96, and the damper hub 94 on the shaft 93 of the rotary damper92. The spacer 102 is sandwiched between the rotary damper 92 and themount 104 by threading bolts to threaded apertures of the mount 104.Thus, the rotary damper 92 is operably coupled to the shaft 80 and thehousing 78.

The rotary damper 92 provides controlled damping of rotational movementof the shaft 80 about the axis of rotation b. The amount of torqueoutput to control damping provided by the rotary damper 92 may bepreadjusted and pre-calibrated to tight specifications. Thus, the rotarydamper assembly 90 a alleviates problems with adjustment and calibrationof counter balance that were typical to conventional counter balancesolutions for portable coordinate measuring machines such as coilsprings, torsion springs, and pistons. Also, the rotary damper assembly90 a provides a counter balance solution that is generally more compactand lighter in weight when compared to conventional counter balancesolutions such as coil springs, torsion springs, and pistons.

FIG. 8 illustrates an exploded view of exemplary base 4 and swivel joint12. The base 4 may house a main printed circuit board (PCB) 158 that mayreceive signals from the various encoder printed circuit boards 36 ofthe CMM 1. The main printed circuit board 158 may also include a powerjack 25 to which a power adapter may be connected to power the CMM 1 andserial communication ports (e.g., USB 152). FIG. 8 also illustrates thebase enclosure 4 a, which has mounted thereon a battery receptacle 26.The CMM 1 may be portable and, therefore, may be operated on batterypower from a battery (not shown) installed to the CMM 1 via thereceptacle 26.

The swivel joint 12 may include housing 28, shaft 30, bearings 32, 34,encoder printed circuit board 36, encoder disk 38, and slip ring 40. Theswivel joint 12 may also include dust covers 42 a-c and various hardwaresuch as the threaded studs 44 a-c and screws 47 a-c. Swivel joints ingeneral are discussed in detail above in reference to swivel joint 16.

FIG. 9 illustrates a perspective view of an exemplary hinge joint 14 (asillustrated in FIG. 7) mounted to a swivel joint 12 and base 4 (asillustrated in FIG. 8). The base 4 includes multiple components such asthe base enclosure 4 a and the base plate 4 b. The base enclosure 4 amounts to the base plate 4 b which, in turn, includes mounting holes 108for fasteners (e.g., bolts) to attach the base 4 to the magnetic holder5 or to a mounting surface MS. The base 4 of FIG. 9 is somewhat typicalof prior art CMM. It adequately allows for mounting the CMM 1 to amounting surface MS and housing of the main printed circuit board (PCB)158. However, this typical design is bulky, expensive, and inelegant.

FIG. 10 illustrates a perspective view of an exemplary hinge joint 14(as illustrated in FIG. 7) mounted to a base assembly 200 including aswivel joint 12 and a base plate 204. Similar to the enclosure 4 a ofthe base 4, the base plate 204 may house the main printed circuit board(PCB) 158 that includes the power jack 25, serial ports (e.g., USB 152),etc. In the illustrated embodiment of FIGS. 10 and 11, the base plate204 is disk-shaped and the main printed circuit board 158 is disposedinside the disk. In other embodiments, the base plate 204 may not bedisk-shaped but instead may be an ovoid, a rectangular prism, etc. butstill have the main printed circuit board 158 disposed inside.

Similar to the plate 4 b of the base 4, the base plate 204 may havemounting holes 208 formed thereon to receive fasteners (e.g., bolts) formounting the base plate 204 to the magnetic holder 5 or to the mountingsurface MS. As can be appreciated from FIGS. 10 and 11, however, theimproved design of the base plate 204 is simpler (fewer pieces), lighter(easier to transport), less bulky, and aesthetically more pleasant. Whencompared to the base 4, this design also minimizes the distance betweenthe mounting plate and the joint 12 (compare the location of joint 12relative to the mounting surface MS between FIGS. 7 and 8), which mayreduce flexing or deformation of the CMM 1 and, thus, improve the CMM'saccuracy.

The mounting holes 208 may be formed to extend through a circular sidewall 204 g from a top surface 204 a (or 204 aa) to a bottom surface 204b of the base plate 204. In the embodiment of FIG. 8, the top surfaces204 aa on which the through-holes 208 are formed, are counterbored tobury fastener head below surface 204 a for aesthetic purposes. Thus, themounting holes 208 may have a top opening formed on the top surface 204a (or 204 aa) and a bottom opening formed on the bottom surface 204 b.

The base plate 204 may also have formed thereon side pockets or holes204 h to allow access to the power jack 25, a USB connector 152, etc.

FIG. 11 illustrates a cross-sectional view of the exemplary swivel joint12 and base assembly 200 of FIG. 10 including the housing 28 and thebase plate 204. FIG. 12 illustrates an exploded view of the exemplarybase plate 204 of FIG. 10. The base plate 204 has the top surface 204 a(or the counterbored top surface 204 aa) that may have formed thereonthe holes 208 (extending through the circular side wall 204 g to thebottom surface 204 b) that receive fasteners for mounting the CMM 1 tothe mounting surface MS. The base plate 204 may have ribs 204 c formedaround the mounting holes 208 for rigidity. In the illustratedembodiment, the base plate 204 has a circular lateral outer surface 204f disposed below the top surface 204 a. The main printed circuit board158 may be disposed inside the circular side wall 204 g, within thecircular lateral outer surface 204 f, below the top surface 204 a, andabove the bottom surface 204 b.

The base plate 204 has a cavity 206 formed thereon with an opening thatopens towards the mounting surface. The main printed circuit board 158is disposed horizontally within the cavity 206 below the top surface 204a (or the counterbored top surface 204 aa). The base plate 204 has acircular lateral inner surface 204 e that encircles the cavity 206. Themain printed circuit board is disposed within the circular lateral innersurface 204 e. The base plate 204 may have a cover plate 210 thatattaches to the base plate 204 to cover the opening to the cavity 206.The cover plate 210 may, for example, be fastened to the base plate 204using screws 212. The main printed circuit board 158 may be mounted tothe cover plate 210 or to the base plate 204 also using screws 212. Thebase plate 204 may also have formed thereon side pockets or holes 204 hto access the power jack 25, a USB connector 152, etc.

The swivel joint 12 may include housing 28, shaft 30, bearings 32, 34,encoder printed circuit board 36, encoder disk 38, and slip ring 40. Thehousing 28 of the joint 12 may be attached to the base plate 204 suchthat a portion of the housing 28, the bearing 32, and a portion of theshaft 30 are disposed somewhat inside the base plate, at least below thetop surface 204 a. The shaft 30 may have an internal opening 30 a (e.g.,0.5″ or 12.7 mm in diameter) that houses the slip ring 40.

The housing 28 may have a circular flange 28 d formed at a distal end ofa cylindrical outer surface thereof and the base plate 204 has acorresponding circular groove 204 i formed at an end of a cylindricalinner surface thereof. The circular flange 28 d engages the circulargroove 204 i.

The encoder printed circuit board 36 and the encoder disk 38 may behoused within the cavity 206 parallel to the main printed circuit board158. This arrangement is particularly space-efficient and compact. Inone embodiment, the gap between the main PCB 158 and the encoder PCB 36is 6 mm. The taller components on the main PCB 158 may be placed nearthe edges of the main PCB 158 (that do not vertically overlap theencoder PCB 36) where the height is larger. In one embodiment, the gapbetween the main PCB 158 and the top inner surface 204 d of the baseplate 204 is 12 mm.

FIG. 13A illustrates a perspective view of an exemplary base assembly200. The base assembly 200 includes the housing 28 and the base plate204. The housing 28 has a barrel portion 28 a whose outer surfaceoperably attaches to one end of the base plate 204. The housing 28 alsohas a port 28 b whose inner diameter 65 engages (e.g., fixedly attachesto) the outer diameter or outer race of one of the bearings 32, 34.

The base assembly 200 may be manufactured from a single block ofmaterial (e.g., steel). FIG. 13B illustrates a perspective view of anexemplary block 280 from which the base assembly 200 may be formed(e.g., machined). In another embodiment, the base assembly 200 mayinstead be casted as a single piece using a mold. Forming the baseassembly 200 as a single piece (e.g., from a single block of materialsuch as the block 280) may offer significant advantages, the mostsignificant of which may be precision. Forming the part as a singlepiece—versus various parts attached together—may reduce the chances ofdistortion, misalignment, imperfections, etc. that could negativelyaffect the part's precise shape. This is why, in the prior art, partssuch as the base assembly 200 were built (e.g., machined) from a singleblock of material. Manufacturing a relatively complex part such as thebase assembly 200 from a single block of material, however, isrelatively expensive. But, in the prior art, there was no choice.

FIGS. 14A and 14B illustrate perspective views of a housing 28 and abase plate 204, respectively. The housing 28 is cylindrical havinginside thereof the port 28 b that engages at least one of the bearings32, 34. The base plate 204 connects the CMM 1 to the mounting surfaceMS. The base assembly 200 may be formed by welding the housing 28 to thebase plate 204. For this purpose, the base plate 204 has a top openinghaving a cylindrical inner surface 204 j that matches the radius of thecylindrical outer surface 28 a of the housing 28. The base plate 204 andthe housing 28 may be held in place with the cylindrical outer surface28 a adjacent the cylindrical inner surface 204 j and welded together.

Welding the housing 28 to the base place 204 may negatively affect theprecision of the resulting base assembly 200 by, for example, distortingthe precision honed bore of the port 28 b. Therefore, the weldingapproach disclosed herein is counterintuitive in the context of CMM,where there is an expectation of a high level of precision. However, thebenefits of this novel approach are significant. For example, it maytake less time and material to machine the two-pieces of FIGS. 14A and14B versus the one-piece of FIG. 13A.

After machining the housing 28 and the base plate 204 from individualblocks, each smaller than the block 280, the two pieces may be weldedtogether with the cylindrical outer surface 28 a adjacent thecylindrical inner surface 204 j. The parts may be welded together usingone of the various known welding methods (e.g., MIG welding, TIGwelding, Laser Welding, etc.) In one embodiment, Laser Welding ispreferred as it causes the least material distortion. The bearing borecan be honed prior to Laser Welding as Laser Welding will not distortthe precision honed bore of the port 28 b.

The resulting, welded base assembly 200 is significantly less expensivethan a single machined part. The resulting, welded base assembly 200 isalso stronger than a single, casted part that tend to be porous and lessstrong than machined parts. The resulting, welded base assembly 200 isalso less expensive that a casted part because casting requires majorinvestment in molds. Furthermore, casting often requires post-castingmachining, increasing the cost per part.

The two-piece welded, base assembly 200 may, by itself, be less precisethan the one-piece machined part of FIG. 13A. The use of such atwo-piece part is, therefore, again, counterintuitive in the context ofprecision CMM.

FIG. 15 illustrates a perspective view of an exemplary measurement probe6 a. Probe 6 a includes a housing 126 that has an interior space forhousing PCB 130 and a handle 128 that has an interior space for housingPCB 125. The housing 126 and the handle 128 are shown in FIG. 9Atransparent for illustration purposes. Housing 126 operably couples tothe swivel joint 24 (see FIGS. 1A-1D). Thus, the probe 6 a rotates aboutthe axis a of the swivel joint 24 and the swivel joint 24 detects theangle of rotation of the probe 6 a about the axis a.

The measurement probe 6 a may also include a probe stem assembly 136having a probe connector 138 at one end and a probe 140 at the otherend. The probe connector 138 connects to the housing 126 and the PCB130. The probe stem assembly 136 may be a touch trigger assembly whichtriggers the capture of the position of the probe 140 when the probe 140touches an object. The PCB 130 receives such a trigger signal andtransmits it as described below. The probe stem assembly 136 may alsohouse electronics such as, for example, an integrated circuit (e.g.,EEPROM) having stored therein a serial number to uniquely identify aprobe stem assembly 136 upon installation to the CMM 1.

Handle 128 may include two switches, namely a take switch 131 and aconfirm switch 132. These switches may be used by the operator to take ameasurement (take switch 131) and to confirm the measurement (confirmswitch 132) during operation. The handle 128 is generally shaped toresemble a person's grip, which is more ergonomic than at least someprior art probes. The handle 128 may also house a switch PCB 134 towhich the switches 131 and 132 may mount. Switch PCB 134 is electricallycoupled to PCB 125 hosting components for processing signals from theswitches 131 and 132. In one embodiment, the PCB 125 includes a wireless(e.g., Wi-Fi, Bluetooth, etc.) transmitter (instead of an electricalconnection to the communication bus of the CMM 1) that wirelesslytransmits take and confirm signals associated with the switches 131 and132 to, for example, a host PC that generally controls the CMM 1.Wireless transmission of the take and confirm signals associated withthe switches 131 and 132 significantly simplifies construction andwiring of the probe 6 a.

The measurement probe 6 a may also include an option port 142 to whichoptional devices such as, for example, a laser scanner (not shown) maybe connected. The option port 142 provides mechanical connections forthe optional devices to be supported by the measurement probe 6 a. Theoption port 142 may also provide electrical connections for the optionaldevices to interface with the communication bus of the CMM 1.

FIG. 16 illustrates a perspective view of an exemplary on-arm switchassembly 10. Switch assembly 10 includes a housing 146 that has opening148 to mount (e.g., clamp) the switch assembly 10 to the arm segment 8or, alternatively to the arm segment 9. The housing 146 has an interiorspace for housing a PCB. Similar to the probes 6 and 6 b, the switchassembly 10 may include two switches, namely a take switch 131 and aconfirm switch 132 that may be used by the operator to take ameasurement (take switch 131) and to confirm the measurement (confirmswitch 132) during operation. The position of the on-arm switch assembly10, and more importantly of the switches 131 and 132, on the arm 2instead of in the handles of the probe 6 allow for the operator to moveand position the measurement probe 6 with one hand and to actuate theswitches 131 and 132 with the other hand while supporting the arm. Priorart coordinate measurement machines required operators to position themeasurement probe and actuate measurement switches in the probe with thesame hand. This is not ergonomic. The on-arm switch assembly 10 is asignificant advance in the coordinate measuring machine field because itprovides a significantly more ergonomic solution as compared to priorart coordinate measurement machines.

The on-arm switch assembly 10 may also house a switch PCB 134 to whichthe switches 131 and 132 may mount or the on-arm switch assembly 10 mayinclude a PCB that incorporates the functionality of both PCB 130 andswitch PCB 134. In one embodiment, the PCB in the on-arm switch assembly10 electrically connects to the communication bus of the CMM 1. Inanother embodiment, the PCB in the on-arm switch assembly 10 includes awireless (e.g., Wi-Fi, Bluetooth, etc.) transmitter (instead of anelectrical connection to the communication bus of the CMM 1) thatwirelessly transmits take and confirm signals associated with theswitches 131 and 132.

FIG. 17 illustrates a block diagram of exemplary electronics for the CMM1. The CMM 1 may include external communication interfaces such as aUniversal Serial Bus (USB) 150 and wireless (Wi-Fi) 152. The CMM 1 mayalso include an internal communication bus (e.g., RS-485) 154. Asdiscussed above, the various joints or axis of the CMM 1 each includes aPCB 36 which has installed thereon at least one transducer configured tooutput an angle signal corresponding to an angle of rotation of thejoint. The PCB 36 may each include a processor 70 for receiving anglesignals from the transducers and/or strain signals from the PCB 112 ofthe rotary damper assemblies 90. The PCB 36 may also include atransceiver 156 to interface with the bus 154.

The PCB 130 of the measurement probe 6, which may carry signals from thetouch trigger probe 140, may also connect to the communication bus 154.The bus 154 may also connect to the option port 142 of the measurementprobe 6 to communicate/control optional devices such as, for example, alaser scanner installed to the option port 142. The PCB 125 of thehandle 128 may wirelessly transmit take and confirm signals associatedwith the switches 131 and 132.

The bus 154 terminates at a main PCB 158 preferably located at the base4 or the base plate 204 of the CMM 1. The main PCB 158 includes its ownmain processor 160 and transceiver 162 for connecting to the bus 154.The main PCB 158 receives the angle signals from the transducers in theCMM 1 and output an agglomeration of the received angle signals via theWi-Fi 150 or the USB 152 to a host PC such that the host PC maycalculate the position of the measurement probe 6 based on thisinformation and other information relating to the CMM 1 (e.g., location,length of arm segments, etc.) The internal bus 154 may be consistentwith RS485. The bus 154 includes, from the main PCB 158's point of view,a pair of bidirectional wires 164 and 166 (A-B Pair, half duplex) or twopairs of unidirectional wires (A-B Pair and Y-Z pair, full duplex).

Definitions

The following includes definitions of selected terms employed herein.The definitions include various examples or forms of components thatfall within the scope of a term and that may be used for implementation.The examples are not intended to be limiting. Both singular and pluralforms of terms may be within the definitions.

As used herein, an “operable connection” or “operable coupling,” or aconnection by which entities are “operably connected” or “operablycoupled” is one in which the entities are connected in such a way thatthe entities may perform as intended. An operable connection may be adirect connection or an indirect connection in which an intermediateentity or entities cooperate or otherwise are part of the connection orare in between the operably connected entities. In the context ofsignals, an “operable connection,” or a connection by which entities are“operably connected,” is one in which signals, physical communications,or logical communications may be sent or received. Typically, anoperable connection includes a physical interface, an electricalinterface, or a data interface, but it is to be noted that an operableconnection may include differing combinations of these or other types ofconnections sufficient to allow operable control. For example, twoentities can be operably connected by being able to communicate signalsto each other directly or through one or more intermediate entities likea processor, operating system, a logic, software, or other entity.Logical or physical communication channels can be used to create anoperable connection.

“Signal,” as used herein, includes but is not limited to one or moreelectrical or optical signals, analog or digital signals, data, one ormore computer or processor instructions, messages, a bit or bit stream,or other means that can be received, transmitted, or detected.

To the extent that the term “includes” or “including” is employed in thedetailed description or the claims, it is intended to be inclusive in amanner similar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim. Furthermore, to the extentthat the term “or” is employed in the detailed description or claims(e.g., A or B) it is intended to mean “A or B or both”. When theapplicants intend to indicate “only A or B but not both” then the term“only A or B but not both” will be employed. Thus, use of the term “or”herein is the inclusive, and not the exclusive use. See, Bryan A.Garner, A Dictionary of Modern Legal Usage 624 (2 d. Ed. 1995).

While example systems, methods, and so on, have been illustrated bydescribing examples, and while the examples have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit scope to such detail. It is, of course, notpossible to describe every conceivable combination of components ormethodologies for purposes of describing the systems, methods, and soon, described herein. Additional advantages and modifications willreadily appear to those skilled in the art. Therefore, the invention isnot limited to the specific details, the representative apparatus, andillustrative examples shown and described. Thus, this application isintended to embrace alterations, modifications, and variations that fallwithin the scope of the appended claims. Furthermore, the precedingdescription is not meant to limit the scope of the invention. Rather,the scope of the invention is to be determined by the appended claimsand their equivalents.

What is claimed is:
 1. A coordinate measurement machine (CMM)comprising: a manually-positionable articulated arm having first andsecond ends, the articulated arm including a plurality of arm segmentsand a plurality of rotary joints; each of the rotary joints from theplurality of rotary joints including: first and second bearings; a shaftthat engages an inner diameter of the first bearing and an innerdiameter of the second bearing, the shaft configured to rotate about anaxis of rotation of the first bearing and the second bearing; a housinghaving at least one port that engages at least one of an outer diameterof the first bearing and an outer diameter of the second bearing; and atleast one transducer configured to output an angle signal correspondingto an angle of rotation of the shaft relative to the housing about theaxis of rotation; the first end including a connector configured toconnect to a measurement probe; and the second end including a baseconfigured to be fastened to a mounting surface for mounting the CMM tothe mounting surface, the housing of at least one rotary joint from theplurality of rotary joints having a cylindrical outer surface thatengages a) the base or b) a connecting portion that connects the atleast one rotary joint to another rotary joint from the plurality ofrotary joints, the housing welded to the base or to the connectingportion.
 2. The CMM of claim 1, wherein the connecting portion connectsthe housing to a shaft of the another rotary joint.
 3. The CMM of claim1, wherein the housing is welded to the base such that at least one ofthe first and second bearings of the at least one rotary joint isdisposed below a top surface of the base.
 4. The CMM of claim 1, whereinthe base has a cavity formed thereon and a main printed circuit board ofthe CMM is disposed within the cavity, and an encoder printed circuitboard associated with the at least one rotary joint is disposed withinthe cavity parallel to the main printed circuit board.
 5. The CMM ofclaim 1, wherein the base has a cavity formed thereon and an encoderprinted circuit board associated with the at least one rotary joint isdisposed within the cavity.
 6. The CMM of claim 1, wherein measurementerror of the CMM introduced by inconsistent welding of the housing tothe connecting portion is reduced by implementation of a kinematic modelbased on a generalized geometric error model.
 7. A coordinatemeasurement machine (CMM) comprising: a manually-positionablearticulated arm having first and second ends, the articulated armincluding a plurality of arm segments and a plurality of rotary joints;an electrical circuit including a main printed circuit board and aplurality of encoder printed circuit boards; at least one of the rotaryjoints from the plurality of rotary joints includes: first and secondbearings; a shaft that engages an inner diameter of the first bearingand an inner diameter of the second bearing, the shaft configured torotate about an axis of rotation of the first bearing and the secondbearing; a housing having at least one port that engages at least one ofan outer diameter of the first bearing and an outer diameter of thesecond bearing; and at least one transducer operably connected to anencoder printed circuit board from the plurality of encoder printedcircuit boards, the at least one transducer configured to output anangle signal corresponding to an angle of rotation of the shaft relativeto the housing about the axis of rotation; the first end including aconnector configured to connect to a measurement probe; and the secondend including a base plate for mounting the CMM, the base plate having acavity with a bottom opening and a top opening that receives the housingof a first joint from the plurality of rotary joints, the housing weldedto the base plate.
 8. The CMM of claim 7, wherein the housing is weldedto the base such that at least one of the first and second bearings ofthe first joint is disposed below a top surface of the base plate. 9.The CMM of claim 7, wherein the main printed circuit board is disposedwithin the cavity, and the encoder printed circuit board is disposedwithin the cavity parallel to the main printed circuit board.
 10. TheCMM of claim 7, wherein the encoder printed circuit board is disposedwithin the cavity.
 11. The CMM of claim 7, wherein the base plate has acircular lateral inner surface that encircles the cavity and the encoderprinted circuit board is disposed within the circular lateral innersurface of the base plate.
 12. The CMM of claim 7, wherein the topopening has a cylindrical inner surface that engages a cylindrical outersurface of the housing.
 13. The CMM of claim 7, wherein the housing hasa circular flange formed at a distal end of a cylindrical outer surfacethereof and the base plate has a corresponding circular groove formed atan end of a cylindrical inner surface thereof, the circular flangeengaging the circular groove.
 14. The CMM of claim 7, the base plateshaped like a disk, the main printed circuit board disposed inside thedisk, the housing partially inserted into a top opening of the disk. 15.A coordinate measurement machine (CMM) comprising: amanually-positionable articulated arm having first and second ends, thearticulated arm including a plurality of arm segments and a plurality ofrotary joints; at least one of the rotary joints from the plurality ofrotary joints includes: first and second bearings; a shaft that engagesan inner diameter of the first bearing and an inner diameter of thesecond bearing, the shaft configured to rotate about an axis of rotationof the first bearing and the second bearing; a housing having at leastone cylindrical portion having inside thereof a port that engages atleast one of an outer diameter of the first bearing and an outerdiameter of the second bearing, and a connecting portion that connectsthe at least one of the rotary joints to another rotary joint from theplurality of rotary joints, the cylindrical portion welded to theconnecting portion; and at least one transducer configured to output anangle signal corresponding to an angle of rotation of the shaft relativeto the housing about the axis of rotation; the first end including aconnector configured to connect to a measurement probe; and the secondend including a base plate for mounting the CMM to a mounting surface.16. The CMM of claim 15, wherein the connecting portion connects thehousing to a shaft of the another rotary joint.
 17. The CMM of claim 15,wherein measurement error of the CMM introduced by inconsistent weldingof the housing to the connecting portion is reduced by implementation ofa kinematic model based on a generalized geometric error model.